Solutions containing noble metal compounds



Patented Nov. 12, 1968 3,410,807 SOLUTIONS CONTAINING NOBLE METALCOMPOUNDS William G. Lloyd, Dover, N.J., assignor to The Lummus Company,New York, N.Y., a corporation of Delaware No Drawing.Continuation-in-part of application Ser. No. 391,005, Aug. 20, 1964.This application Feb. 9, 1967, Ser. No. 614,788

10 Claims. (Cl. 252--429) ABSTRACT OF THE DISCLOSURE Stable, homogeneoussolutions of compounds of Group VIII noble metals, monoor poly-hydricalcohols and 0.1- 12 percent (volume) of water are suitable forcatalytic oxidation of compounds including olefins, aromatichydrocarbons, carbon monoxide and sulfur dioxide. Processes for sooxidizing CO to organic carbonates and 80;, to organic sulfates.

This application is a continuation-in-part of my application Ser. No.391,005, filed Aug. 20, 1964, and now abandoned; of applications filedJuly 23, 1965, namely, Ser. No. 474,460, 474,461 and 474,506, each ofwhich is a continuation-in-part of Ser. No. 391,005; and of Ser. No.534,419, filed Mar. 15, 1966.

This invention relates to solutions containing noble metal compounds.More specifically, it has to do with stable, homogeneous solutionshaving catalytic activity for a plurality of chemical reactions.

The catalytic activity of the Group VIII metals has been long recognizedand many catalysts containing these metals are used commercially in, forexample, hydrogenation and oxidation processes. Their activity has beenascribed to the ability of these metals to form coordinate covalentbonds with various organic reactants and to their labile valencestructure. The former property gives rise to chemisorption while thelatter gives rise to single electron transfer activation of, forexample, H and Such catalysts are, however, costly, not only because thenoble metals per se are rare, but also because in the metallic form onlya tiny fraction of the metal is catalytically active. That fraction ofthe metal which is active must first of all be on the surface of thesolid catalyst. Since reactants do not have access to deep lying atomsin the metal structure, they are replaced by less costly materials,i.e., supports. Nevertheless, even with a noble metal layer a few atomsdeep, only those atoms whose valences are unsaturated by adjacent atomsexert catalytic activity. Thus, the density of so-called active sites isrelatively low. Furthermore, these sites are subject to poisoning notonly by irreversible adsorption of various materials but also by theannealing effect that is inevitable at the high temperatures at whichsuch catalysts are used. The need for these high temperatures, ofcourse, results from the relatively poor activity of massive solidcatalysts which has its origin in the reasons just outlined.

Atomic level dispersions suitable for catalysis can be made bydissolving salts of the appropriate Group VIII metals in a liquidmedium. The reaction to be catalyzed would then be conducted in thismedium. Both the reactants and the catalyst salt must, therefore, besoluble in the medium. Water has been used as a medium in, for example,the process in which olefins are oxidized to carbonyl compounds in thepresence of palladium salts. However, water has many serious drawbacks.Not only are organic materials and simple palladium salts sparinglysoluble in it, but palladium II salts are hydrolyzed to insoluble oxidesand hydroxides.

A common arttifact to overcome the lack of solubility of transitionmetal salts in water is to add solubilizing agents which are materialscapable of forming complex ions with the metal. Thus, a homogeneousaqueous solution 0.001 M in PdCl can be made if the solution is alsomade 0.002 M in LiCl. (M signifies gram-moles per liter). Even thissolution, however, deposits a sludge in three hours at room temperature,as a result of hydrolysis, for example:

Pd(H O) Cl +H O- Pd(H 0) (0H)Chi-H 0 Although such precipitation can beretarded by operating in an acidic environment, so doing greatlyincreases corrosion problems.

Although it is reasonable to expect that aqueous solubility can also beincreased by use of high proportions of complexing materials, it is notso obvious a priori that the resulting solutions have poor catalyticactivity. It is thought that this situation arises because thesolubilizing agents pre-empt those coordination sites which are normallyoccupied by water prior to hydrolysis. These same sites, however, arethose to which the reagent would bond in order to be activated. Inaqueous media one, therefore, is faced with several problems. In orderfor the organic reactant to be activated, it must dissolve and becoordinated by the metal. In order to maintain the metal in solution, itmust be coordinated by a solubilizing agent. This solubilizing agentmust have suflicient affinity for the metal and/or be present insuificient concentration so that it can displace water from the metalscoordination sphere. The organic reactant neither has sufficientaifinity for the metal nor dissolves in sufficient amount to displacethe solubilizing agent so activation is poor at best.

It is an object of the present invention, therefore, to provide stable,homogeneous solutions containing noble metal compounds. Another objectis to provide such solutions having catalytic activity for a pluralityof chemical reactions. Another object is to provide solutions of noblemetal of atomic dimensions, thereby gaining more eflicient use of suchrelatively expensive metals. A further object is to provide catalystcompositions possessing relatively long term use and storage stability,and not subject to poisoning by annealing. Still another object is toprovide techniques for catalyst preparation which are relativelyinexpensive and which do not require special equipment or criticalprocessing control. Additional objects of the invention will be apparentfrom the following description.

In accordance with the present invention, therefore, there are providedstable, homogeneous solutions comprising:

(a) A compound of noble metal of Group VIII of Mendeleeffs PeriodicTable,

(b) A monoor poly-hydric alcohol, and

(c) From about 0.1 to about 12 percent by volume of water.

In the solutions or reagents contemplated herein, a compound of a noblemetal of Group VIII of Mendeleetfs Periodic Table is used. Typical ofsuch metals are: palladium, irridium, ruthenium, rhodium, platinum andosmium. The metals are used in the form of a metal compound. Anionsassociated with the metals can be of a wide variety, with halides beingpreferred. Catalytic amounts of metal compound will generally be fromabout 0.0001 to about 0.01 molar proportion with respect to the organicreactant or reactants employed.

Particularly preferred of the noble metal compounds is palladouschloride.

The noble metal compound is preferably used with a promoter capable ofchanging the valence of the reduced noble metal to a higher valencestate, particularly in continuous operations. Representative is cupricchloride.

Others include such redox systems as compounds of metals having variousoxidation stages, namely: compounds of copper, silver, tin, lead,cerium, mercury, nickel, iron, etc. Anions associated with the metalscan be of wide variety including nitrates, acetates, andtetrafluoroborates, with preference being accorded to tetrafluoroboratesand to halides and, particularly, to chlorides. Representative promotersinclude: cupric chloride, bromide, fluoride, tetrafluoroborate,trichloroacetate, acetate, citrate, acetylacetone, benzoate,ferrocyanide, and nitrate; cuprous iodide, thiocyanate, and cyanide;ferric and ferrous chlorides; mercuric chloride; cobaltous chloride; andsilver acetate. The molar ratio of promoter to noble metal compound isfrom about 0.121 to about 100:1.

Suitable organic redox systems include the following, with a promoterbeing recited and its reduced counterpart being given parenthetically:benzoquinone (hydroquinone), o-benzoquinone (cathecol); and chloranil(tetrachlorohydroquinone) It has also been found that vicinal diketonesare particularly advantageous promoters. Typical of such diketones are2,3-butanedione (diacetyl); 3,4-hexanedione; and LZ-diphenylethanedione(benzil).

Thus, diketone promoters include vicinal diketones and diketones inwhich the keto groups are separated by a l l C=C;

group.

Particularly preferred are benzil and 'chloranil.

Compounds capable of oxidation to vicinal diketones are also useful aspromoters. Such compounds are illustrated by: acetoin (which is oxidizedto diacetyl); benzoin (which is oxdized to benzil); and ascorbic acid(which is oxidized to dehydroascorbic acid). Other promoters are4-methoxycatechol and 4-tertiarybutyl catechol.

Concentration of vicinal diketone or its precursor ranges from about 1:1to about 100:1, based upon the noble metal compound.

Iodine is also useful as a promoter.

Preferred promoters, however, are chlorides, bromides and iodides ofmetals of Groups VIII and I-B of Mendeleeffs Periodic Table, and cuprouschloride is particularly preferred.

Alcohols useful herein include monohydric or polyhydric and mixturesthereof. Primary, secondary and tertiary monohydric alcohols can beused. Representative alcohols include: methyl, ethyl, propyl, butyl,secondary butyl, isobutyl, tertiary butyl, pentyl, hexyl, benzyl andethylene chlorohydrin. Polyhydric alcohols are typified by vicinaldiols: ethylene glycol, propylene glycol, 2,3-butylene glycol,3-chloropropanediol-1,2; homovicinal diols; propane-1,3; non-vicinaldiols: hexanediol-1,6; other polyols; glycerine, pentaerythritol,sorbitol, sucrose, mannitol, 1,4-dihydroxymethyl benzene,2-methyl-2,4-pentaediol, 1,1-dimethylol ethylene, 1,4-cyclohexanedimethanol, 2,2, 4,4-tetramethylcyclobutane-1,3-diol, 2,2-propylidenebis (4-benzyl alcohol), 4,4-dimethylolcyclohexene.

As indicated above, water comprises from about 0.1 to about 12, andpreferably 0.56, percent by volume of the solutions. Water can be addedper se or can be present in part or whole with the alcohol or as waterof hydration of noble metal compound and/ or promoter. There is no needto use an anhydrous solution, as by using an anhydrous alcohol. The costof removing the last traces of water from an alcohol is avoidedtherefore. Since water is known to be a stronger ligand than alcohol, itwould be expected that even with trace amounts of water, a catalystsolution would resemble a catalyst formed with only water as the liquidmedium rather than one formed with an anhydrous alcohol. Surprisingly,the catalyst solutions formed with an alcohol and 0.112 percent byvolume have some of the characteristics of solutions formed with ananhydrous alcohol.

As demonstrated hereinafter, quantities of water greater than about 12volume percent are disadvantageous. Preferred solutions are those inwhich the water content is between about 0.5 and about 6 percent byvolume.

Advantages of the solutions containing 0.1-l2 percent of water areillustrated by monohydric alcohol media and olefin oxidation. The olefinoxidation product is usually a free carbonyl compound, as a methylketone. In such an oxidation, there are a plurality of advantages. Theketone, rather than a corresponding ketal, is usually the desiredproduct; and, it is advantageous to form the desired product directly,thereby avoiding the need for a separate ketal hydrolysis step. Theketone product can generally be separated readily from the olefinreaction mixture, while the corresponding ketal product is separatedwith greater difliculty. For example, in the oxidation of propylene inethyl alcohol (boiling point, B.P., 78.4 C.), with water present, theproduct is the desired acetone (B.P., 56.5 C.), which is readilyisolable from the aqueous ethanol mixture by distillation. In contrast,under anhydrous conditions, the product is 2,2-diethoxypropane (B.-P.,114 C.), which cannot be isolated by distillation except by anuncconomical distillation of the entire solvent charge prior to productseparation from the catalyst. Moreover, when the oxidation is carriedout in the presence of 0.1-12 percent of water, to form carbonylproducts, no water of reaction is formed. Consequently, it is notnecessary to include a continuous dewatering step in the oxidationprocedure:

R'CH=CHR+1/20 RCH COR" (ROH, H O, catalyst, reoxidant are present).

Under anhydrous conditions, however, formation of an acetal or ketalinvolves the concomitant formation of equimolar amounts of water, whichmust be removed promptly in order to maintain an anhydrous system:

(Catalyst and reoxidant are present).

In the illustrative equations, R represents alkyl groups and R and R"represent hydrogen or alkyl groups.

It is surprising to 'find organic materials, i.e., alcohols, to have agreater solvent power for noble metal salts than water. For example, amethanolic solution 0.001 M in PdCl and 0.002 M in LiCl remained clearfor over 15 weeks. Even more concentrated solutions were similarlystable and furthermore the addition of small amounts of water to thesesolutions did not effect visible hydrolysis. Thus, methanolic solutionscontaining up to 10 volume percent water and 0.05 mole PdCl per literand 0.10 mole LiCl remained clear indefinitely while with 30 percentwater, precipitation did not occur before 3 weeks. Of course, thesemethanolic solutions are excellent solvents for organic reactants sothey present a priori an ideal combination of properties.

Not only do these lower alcohols constitute unique media for makinghomogeneous stable solutions of group VIII metals, but the resultingsolutions are unique catalysts. Other organic media either do notdissolve Group VIII metals or their solutions are not catalytic. Knownreactions in which alcoholic solutions of Group VIII metals arecatalytic include: oxidation of ethylene to acyclic and alicyclicacetals; oxidation of higher ole-fins to acyclic and alicyclic ketals;oxidation of primary alcohols to aldehydes and esters; oxidation. ofsecondary alcohols to ketones; and oxidation of benzenes to phenols.These reactions are described in related copending applications U.S.Ser. Nos. 391,005, filed Aug. 20, 1964; 474,460, 474,461 and 474,506,filed July 23, 1965; and 534,419, filed Mar. 15, 1966.

In addition, the alcoholic solutions or reagents of this invention arealso advantageous catalytically for the oxidation of carbon monoxide toorganic carbonates and of sulfur dioxide to organic sulfates. Theseoxidations are illustrated hereinbelow.

The utility of alcoholic solutions of Group VIII metal salts containingsolubilizing agents can be further enhanced by selecting thesolubilizing agent from the group consisting of easily oxidizedmaterials, notably polyvalent metal salts and certain reduciblebifunctional organics. These materials are reduced in preference to theGroup VIII metal. Thus, for example, in the oxidation of ethylene by analkali metal chloropalladate, for example lithium chloropalladate,according to:

ladium. Since the hypothetical product salts can exchange withadditional cupric chloride according to:

It is equally apparent that only a trace of noble metal is required.

Homogeneity is desirable not only from the point of view of catalystefficiency but also because of the well known difliculties in handlingheterogeneous media on an industrial scale. Not only are they difficultto transport but their heterogeneity per se complicates measurement andcontrol.

The following examples are illustrative of the invention. However, it isto be understood that the invention is not to be construed as limited tothe particular materials and conditions recited therein.

Example 1 Ethylene was reacted, in a glass vessel, in an alcoholicreagent solution containing approximately 0.5 percent by volume ofwater. Thus, 500 ml. of ethylene glycol containing water and 0.06 M inpalladous chloride, was stirred for two hours at 50 C. under oneatmosphere of ethylene, in the course of which palladium metalprecipitated and plated on most of the glass surfaces. Analysis of thereaction mixture showed the formation of mg.-moles (50 percent oftheoretical) of 2-methyl-1,3-dioxolane, along with a very small amountof free acetaldehyde.

Example 2 Ethylene reacts readily with alcoholic palladous chloride atmoderate temperatures, with or without the presence of a reoxidant or ofmolecular oxygen. Thus, 500 ml. of ethyl alcohol, 0.03 M in palladouschloride and 1.0 M in cupric nitrate trihydrate, was stirred for twohours at 50 C. under one atmosphere of ethylene. The water content ofthe alcoholic solution, by virtue of the water of hydration of thenitrate, is approximately 5.4 percent by volume. In the presence of theexcess reoxidant, cupric nitrate, there was no deposition of metallicpalladium, and the reaction mixture was found to contain 67 mg.- moles(about 450 percent of theoretical, basis palladium) of acetaldehydediethyl acetal.

Example 3 The use of molecular oxygen and of moderate superatmosphericpressures accelerates greatly the oxidation of ethylene. Thus, a chargeof 200 ml. of ethylene glycol, 0.028 M in palladous chloride and 0.586 Min cupric chloride dihydrate, on being stirred at 50 C., under a 2:1ethylene/oxygen mixture at an initial pressure of 300 p.s.i.g.,underwent a brisk exothermal reaction, the pressure falling to oneatmosphere in thirty minutes. Water content of the alcoholic reagent isabout 2.5 percent by volume. After forty minutes, the product mixturewas found to contain 1.26 rug-moles of 2-methyl-1,3-dioxolane along with13 mg.-moles of free acetaldehyde. This higher conversion,notwithstanding the viscous glycol medium, shows that the regenerativereactions proceed efliciently, since this corresponds to a 2500 percentconversion based upon charged palladium, and a 216 percent conversionbased upon combined palladium and copper salts.

Example 4 1,4-butanediol not only is a reactive alcoholic medium butalso readily forms 7-membered ring products, that is, the 2-substituted1,3-dioxepanes. Accordingly, 1.4- butanediol containing 0.028 Mpalladous chloride and 0.586 M cupric chloride dihydrate, on beingstirred for forty minutes at 50 C. under (initially) 300 p.s.i.g. of a2:1 ethylene/oxygen mixture, reacted smoothly to produce only a trace offree acetaldehyde along with 81 ml./ liter of 2-methyl-1,3dioxepane,identified by infrared spectrum and molar refraction. In a similar runwith 1,5- pentanediol, a much smaller amount (1.6 ml./ liter) of the8-membered ring compound, 2-methyl-1,3-dioxocane, was obtained. With1,6-hexanediol oxidation occurred, most probably to form high-boilingacyclic acetals. Only one small product peak (perhaps the 9'memberedring acetal, 2-methyl-1,3-dioxonane) was detectable at the uppertemperature limits of the chromatographic analysis system which wasused.

Example 5 In a glass shaker-reactor, with three atmospheres of oxygen,20 volume percent of 1-octene (1.285 M) in npropyl alcohol was convertedto octanones in the presence of 0.02 M PdCl and 0.1 M CuCl .2H O. Waterpresent with the alcohol and in the form of water of hydration of thecupric chloride, constituted approximately 0.6 percent by volume of thereagent solution. Reaction was carried on for two hours. The product wasanalyzed by vapor phase chromatography, which indicated that the yieldswere as follows: 67.5 percent 2- octanone, 8.9 percent 3-octanone and2.7 percent 4-octanone, based on all octanones formed. This correspondsto conversions of l-octene to 85 percent Z-octanone, 11 percent3-octanone and 3.5 percent 4-octanone.

Example 6 Styrene was oxidized at a 0.723 M solution in a variety ofalcohols containing PdCl 0.02 M, CuCl 0.04 M and Cu(NO 0.06 M, for twohours at 30 C. under three atmospheres oxygen pressure. Water content ofthe alcoholic reagent solution, in each instance, was approximately 0.7percent by volume. The conversions of styrene in methyl, ethyl, n-propyland n-butyl alcohols were 71 percent, 68 percent, 32 percent and 25percent, respectively. The ratio of acetophenone to phenyl-acetaldehyde(occurring primarily as the corresponding acetal), in these mixedchloride-nitrate systems remaindled close to 1.2 for all four systems,while the amount of side-reaction to form benzaldehyde was only 5percent with methyl alcohol but 18 percent with ethyl alcohol. If bothacetophenone and phenyl-acetaldehyde are counted as product, the yieldsfor the four alcohols, in order of increasing chain length are percent,82 percent, 91 percent and 96 percent. The conversion-yield products are67 percent, 56 percent, 29 percent and 24 percent, respectively. Forthis series, therefore, on the basis of conversions and yields in thesevery mild styrene oxidations at 30 C., methyl alcohol is preferred overthe other alcohols.

Example 7 3-chloropropanediol (obtained by hydrolysis ofepichlorohydrin) reacts to give the corresponding2-substituted-4-chloromethyl1-1,3-diozolanes, of interest as chemicalintermediates. To 20 ml. of a solution of 0.5 M CuC1 and 0.5 M Cu(BF in3-chlor0propanediol were added 5.0 ml. styrene and 1.0 mg.-molepalladous chloride. Water content of the alcoholic reagent solution wasabout 8 percent by volume. The resulting mixture was shaken well andallowed to stand overnight at 53 C.,

whereupon most of the styrene was found to have been converted to2-methyl-2-phenyl-4-chloromethyl-1,3-dioxolane, isolated as the majorproduct (77 percent yield) along with some free acetophenone (6 percent)and a secondary product believed to be the isomeric 2-benzyl-4-chloromethyl-1,3-dioxolane (14 percent yield).

Example 8 20 milliliters (ml) of acrylonitrile and 100 ml. of methylalcohol were added to 1.8 grams (0.01 mole) of palladous chloride and1.98 grams (0.015 mole) of cupric chloride dihydrate in a stirred,stainless steel autoclave of 250 ml. capacity. The clave was pressuredto 100 p.s.i.g. with oxygen, heated to 100 C. and maintained at thattemperature for three hours, with continuous stirring and with severaloxygen additions to maintain pressure. The water content of the chargeto the clave exclusive of the acrylonitrile was approximately 1.5 percent by volume. After cooling the reaction mixture, it was filtered toremove inorganic solids therefrom. The remaining liquid reaction mixturewas analyzed on a preparative gas chromatograph (Wilkens Aerograph ModelA-700), using a ten percent Carbowax 20M column (20 x at 140 C., with ahelium flow rate of 140 mL/min. Under these conditions, a single majorproduct was obtained; this represented about 90 percent of all products. Infrared analysis, elemental analysis (C H O N), boiling point(capillary method) of 195 C. at 764 mm., refractive index white light at25.0 C.) of 1.4122: 0.0001, density at 25 C. of 1011:0005, massspectrometric analysis, and nuclear magnetic resonance spectroscopy, alltaken together indicate that the product is cyanoacetaldehyde dimethylacetal.

Example 9 0.35 gram of PdCl and 0.85 gram of CuC1 .2H O were added to 10ml. of acrylonitrile. The resulting mixture was diluted to 50 ml. withreagent ethylene glycol in a 250-ml. capacity stainless steel bomb. Thebomb was sealed, purged with oxygen, and pressured to 30 p.s.i.g. withoxygen. The bomb was heated, while shaken, to 85 C. and was somaintained for a two-hour period, during which time a pressure drop of12 p.s.i.g. was recorded. The reaction mixture was cooled, and wasdischarged from the bomb by decanting clear liquid from a precipitate ofinorganic salts.

The water content of the charge to the bomb exclusive of acrylonitrile,was approximately 3.8 percent by volume.

The liquid product was analyzed with a F&M Model 720 gas chromatograph,using an eight-foot analytical ethylene glycol succinate column at 150C. The chromatograrns showed an extremely clean reaction implying anear-quantitative yield, with a single peak appearing at 13.4 minutesfor analytical Samples, and 13.5 to 15.0 minutes for larger samples. Theamounts of reaction product in this run, based upon integrated areas ofthe chromatograms, is 6.2 percent by weight. Infrared analysis andelemental analysis (C5H7O2N) indicate that the product is1,3-dioxolane-2'acetonitrile, namely:

. 8 Example 10 1,3-propanediol (40 ml.) and acrylonitrile (10 ml.) weremixed in a 300-ml., glass reactor (a Parr Low Pressure HydrogenationApparatus) together with palladous chloride (0.35 gram) and cupricchloride dihydrate (0.85 gram). The reaction charge, excluding theacrylonitrile, had a water content of about 2.5 percent by volume. Theresulting mixture was heated for three hours at 100 C., with continualshaking and at a pressure of 2535 p.s.i.g. of oxygen. Upon cooling toabout 20 C.25 C., the resulting homogeneous reaction mixture was foundto contain, unreacted glycol, about 25 percent of unreactedacrylonitrile and a single product identified as 1,3-dioxane-2-acetonitrile. Identification was made by elemental analysis, infraredspectrum and refractive index (11 1.4462. Conversion was approximatelypercent.

Example 11 Cyclohexene is oxidized readily by palladous salts inmonohydric alcohols to cyclohexanone, and in dihydric alcohols to thecorresponding spiroketal. With four volumes of ethyl alcohol, 0.028 MPdCl and 0.117 M CuCl .2H O at 30 C. for two hours, cyclohexeneunderwent a 12 percent conversion to cyclohexanone, with no otherproducts detectable. Water content of the charge, exclusive ofcyclohexene, was about 0.7 percent by volume. Similarly, with fourvolumes of ethylene glycol and five volumes of 1,4-dioxane (as aneutralizing solvent and thinner), cyclohexene in two hours at 50 C.with the same catalyst system containing about 0.4 percent by volume ofwater, underwent a 10 percent conversion to the ketal, 1,4-dioxaspiro(4.5) decane, with no side products detectable. In a similar run with1,3-propanediol containing about 5 percent by volume of water, cyclohexene was oxidized to a mixture of 1 part cyclohexanone and 3 parts1,5-dioxaspiro (5.5) undecane.

Example 12 TABLE I Cyclohexanono Run Rcoxidant; Formed, No. Vols/100Vols.

cyclohexene 94 Aeetoin 11 Copper Aeetylacetouate, CII(C H O2)2.. 13Benzil 13 108 1,4-naphthoquiuone 2.5

Example 13 The effect of water content is shown by several runs withn-propyl alcohol in a moderate pressure glass shaking reactor at C. fortwo hours. n-Propyl alcohol was used with 0.02 M PdCl and 0.1 M Cu(NO.3H O, with three atmospheres of oxygen.

As shown in the following tabulation, reaction of the alcohol to formpropionaldehyde and n-propyl propionate is inhibited markedly byemploying relatively large amounts of water.

Water Con- Propionaldehyde, moles/kg. n-Propyl tent, Percent propionate,

by Vol. Total As aeetal Net total moles/kg.

9 Example 14 The elfect of Water content upon the oxidation ofcyclohexene to cyclohexanone at 50 C. in ethyl alcohol is shown in TableII given below.

TAB LE II Water Content a Two hour runs in glass shaker-reactor under 3atmospheres of oxygen, wlth PdCig 0.02 M and CuCl; 0.1 M; each run ml.of cyclohexene., water as indicated, and ethanol q.v. 50 ml.

g Reaction mixture contained two phases; assays made upon both p ases.

u Basis: Total olefin charged.

Example 15 Neopentyl alcohol (2,2-dimethyl-1 propanol) is oxidizedreadily at 90 C. for two hours in the reactor identified in Example 11,under three atmospheres of oxygen, with PdCl 0.02 M and Cu(NO .3H O 0.1M. Water content of the materials charged to the reactor wasapproximately 0.8 percent by volume. Formed in this reaction was amixture containing 1.4 moles/kg. of pivalic aldehyde and 0.3 moles/kg.of a new compound, pivalic aldehyde dineopentyl acetal. The latter ischaracterized by: n 1.4092; 41 0.803; Mr-calculated 74.76, found 75.27.Another product, most probably neopentyl pivalate, was formed in anamount of 0.02 mole/kg.

Example 16 A solution of volume percent benzene in ethylene glycol wascharged to an autoclave. Palladium chloride (7 grams/liter) and CuCl.2I-I O (17 grams/liter) were added. Exclusive of benzene, the materialscharged to the autoclave contained about 0.9 percent by volume of water.The autoclave was heated for one hour at 110 C., under a pressure of 3-6atmospheres of oxygen. The autoclave was cooled and the resultingreaction product was discharged therefrom. Phenol was recovered from thereaction product in a yield in excess of about 80 percent by weight, ata conversion of about two percent per pass based upon benzene charge.

Example 17 Secondary butyl alcohol is oxidized to methyl ethyl ketone asthe sole product, when employed in the reactor identified in Example 11for two hours. Here again, the charge to the reactor included PdCl 0.02M,

0.1 M, and three atmospheres of oxygen. Water content was 0.8 percent byvolume. At temperatures of 70 C., 90 C. and 110 C., the yield was 0.39,0.74 and 1.2 moles/kg, respectively.

In contrast, under identical conditions at 70 C., 80 C. and 90 C.,tertiary butyl alcohol was completely unreactive.

Under conditions identical with those used for secondary butyl alcoholat 90 C., cyclohexanol was converted to cyclohexanone (0.23 mole/kg.) asthe sole product.

Example 18 As indicated above, aqueous alcohols are unusually effectiveas organic media for the catalyst or reagent systems contemplatedherein. For example, benzonitrile has been found to be an ineffectivesolvent-medium for the oxidation of cyclohexene. The catalystcomposition co mprises PdC1 0.02 M and CuCl .2H O 0.1 M, and has a watercontent of about 0.3-0.5 percent by volume. Similar conversions weretried at 50 C. with a variety of other non-alcoholic media. Nosignificant reaction occurs when the solvent medium is dioxane, aceticacid, dimeth- 10 yl sulfoxide, dimethyl formamide, propylene carbonate,chlorobenzene or carbon tetrachloride.

Quantitative data is set out in Table III below.

TABLE IIL-OXIDATION OF CYCLOHEXENE BY PAL- LADIUM (II) IN NON-ALCOHOLICMEDIA Conversion of a Two hour oxidations in a glass shaker-reactorunder 3 atmospheres oxygen pressure; 10 volume percent (0.985 M)cyclohexene in the indicated so l vgitowih PdCl2 0.02 M and 011012211200.1 M, reacted at 50 C.

Example 19 Alcohols are much more advantageous than water with respectto the formation of stable solutions of PdCl This is indicated in TableIV below.

TABLE IV.SOLUTTON STABILI'IIES OF PC1012 IN METHYL ALCOHOL-WATER SYSTEMSVol. Percent H3 D 2 D 5 D21 105 D222 rs. ays ays ays Days a 3 1130 OHH20 y IdCl2 0.05 M and M01 0.1 M

Nil 100 O K O K O K O K P PT 70 30 O K 0 K O K O K PPT 10 O K 0 K O K OK O K O K 96 4 O K 0 K O K O K O K O K 98 2 OK OK 0 K OK OK OK 99 1 OKOK OK 0 K O K OK 100 Nil OK OK OK 'OK OK OK Peon 0.1 M and LiCl 0.02 M

Nil 100 O K 70 30 OK 90 10 OK 96 4 OK 98 2 OK 99 l K 100 b Nil OK Pd Clz0.001 M and LiC10.002 M Nil 100 70 30 90 10 96 4 OK Trace Trace TrgceP191 98 2 OK OK K Trace Trace PPT 99 l O K 0 K O K Trace Trace PPI 100 hNil 0 K O K O K 0 K K O K All solutions were stored in clearborosilicate glass bottles tightly capped and away from direct sunlight,at ambient temperature (about 28 C. at all times). OK" signifies astable solution; PP'I signifies a precipitate has formed.

b This methyl alcohol contained approximately 0.1% (by volume) or;water, and when the salts were dissolved therein contained 0.1-0.2% o waer.

EXAMPLE 2O Palladous salts, for example, PdCl dissolved in alcohols, areactually different from similar solutions in water. This can be shownnot only functionally, as with the examples given above, but in terms ofthe most basic measurements on the molecular level, namely, absorptionspectra.

Ultraviolet and visible spectra of dilute samples of palladous chloridesolutions were obtained with a Beckman Model DK-Z recordingspectrophotometer, using a fast scan with a 1.000-cm. quartz cell, andthe output signal being balanced against that from a matched referencecell containing aqueous methanol of the same composition. Results ofthese spectrophotometric determinations are shown in Table V below.

TABLE V.ULTRAVIOLET AND VISIBLE ABSORPTION OF DILUTE SOLUTIONS OFPALLADOUS CIILO a Measurements at 26 C. with aqueous methyl alcohol ofmatching composition in the reference cell, maximum concentrations ofPdCl 0.02 percent weight/volume and 0.008 percent weight/volume of LiCl;wavelength maxima in millimicrons; extinction coeilicients calculated asthe quotients of the negative logarithm of transmittance and themolarity, i.e.,

logro (l-cm. cell transmittance) (PdOlz cone. in moles/liter) The datagiven above show three strong maxima associated with aqueous-solvatedpalladous chloride, at 202, 303, and 418 millimicrons. All three maximadisplay bathochromic shifts of 110220 Angstrom units as the aqueousmedium is replaced by a methyl alcohol medium, that is, as the solutespecies changes from hydrated palladium (II) chloride to methylalcohol-solvated palladium (II) chloride. This consistent bathochromicshift in going from hydrated palladium (II) to methanol-solvatedpalladium (II) is most resonably interpreted as denoting a decrease inthe metal-to-ligand binding energy. In terms of gross chemical behavior,this implies that alcohol-solvated palladium (II) is more bare, moresusceptible to attack by a ligand of moderate activity, and hence morechemically reactive than the more strongly solvated aquopalladium (II)complexes.

This reasoning is supported by comparative efficiencies of palladium(ID-catalyzed oxidations of olefins in alcohol and in water underparallel conditions as shown in Table VI below.

and percent cyclohexane. In the parallel oxidation with ethanol,however, not only did the desired oxidation proceed much more rapidly,but the disproportionation of olefin was sharply inhibited, residualhydrocarbon con sistent of percent cyclohexene, 13 percent benzene and12 percent cyclohexane. Acrylonitrile, one of least reactive olefinsstudied, reacted smoothly in methyl alcohol at 85 C. to afford a 40percent conversion to the dimethyl acetal of cyanoacetaldehyde; but aparallel oxidation attempted in water gave no product discernible bychromatographic examination. One of the most reactive olefins, ethylene,reacts readily in 40 minutes at 50 C. in alcoholic or aqueous systems;in glycol, however, the ethylene is completely consumed in this period,while in water under parallel conditions only 25 percent of the chargedethylene is reacted. Furthermore, since the prodnot from the oxidationin glycol is a stable compound, 2-methyldioxolane, it is not necessarythat it be removed as formed. Under these static conditions whereinproduct is subjected to conditions fostering various secondaryreactions, only 19 percent of the original acetaldehyde formed in theaqueous reaction is collected as acetaldehyde; while the yield ofZ-methyldioxolane from the parallel run in glycol is over 96 percent.The foregoing data indicate the olefin reaction rates to be generallymuch higher in alcoholic media than in water.

The effects of water upon the alcohol-solvated palladium (II) oxidizingsystem are in general colligative. Added water may affect the productbalance, and at levels as high as 12 percent will adversely affectoxidation reaction rate. Homogeneity of the alcohol systems, anotherdistinct advantage over aqueous systems, is not likely to be impaired bythe presence of small amounts of water.

Example 21 2,5-dihydrofuran is oxidized readily to give thecorresponding ketal of 3-oxotetrahydrofuran. Thus, an 8.3% (v./v.)solution of dihydrofuran in ethyl alcohol containing 0.02 M PdCl and 0.1M CuCl reacted for two hours at 50 C. under oxygen, underwent an 97%conversion. The water content, exclusive of dihydrofuran, is about 0.6percent by volume. The yield of 3,3-diethoxy- TABLE VI.-COMPARATIVEEFFICACIES OF IALLAD%EMW(XI%)E-ATALYZED OLEFIN OXIDATIONS IN ALCOHOL ANDProducts Formed Volume Run No. Olefin Percent T., C. PdClz, M CuCh, MCouver- Conver- Diluent Carbonyl Product Alcohol sion in S1011 1nAlcohol, Water, Percent d Percent 205-6 l-octene 50 50 0.02 0. 1Octanoue Methyl 48. 8 1. 7 d 30 0.018 0.1 do do i 03 2.5 60 0.018 0.1.dO 72 4.5 50 0.2 Nil Cyclohexanone 22 1. 7 50 0.02 0.1 (O do 52 0.13 0.04 0. 03 Cyanoacetaldehyde- Methyl b 40 Ethylene 50 0. 04 0.4Acetaldehyde Ethylene glycol... 21

a Two hour runs in glass shaker-reactor under 3.0 atmospheres of oxygen,except as noted otherwise.

b As cyanoacctaldehyde dhncthyl acetal (no other product discerned).

c 40 minute runs in stirred autoclave charged with 240 p.s.i. ethyleneand 75 p.s.i. oxygen.

Under various conditions, 1-octene is oxidized in methanol to octanonein conversions of 42-72 percent, while under parallel conditions inwater the conversions are all less than 5 percent. Indeed, with theconditions permitting conversions in water as high as 5 percent, theformation of side products was noticeable. Cyclohexene is oxidized tocyclohexanone under model condition to the extent of '52 percent inethyl alcohol, and less than 1 percent in a parallel aqueous reaction.In the absence of a cupric reoxidant, 22 percent of the chargedcyclohexene is oxidized by Pd(II) in ethyl alcohol, while less than 2percent is converted in a parallel aqueous reaction. In this latter pairof reactions, furthermore, the reduced zero-valent palladium metal, apowerful disproportionation catalyst, tends to convert cyclohexene to amixture of cyclohexane and benzene. In the aqueous oxidation, theunreacted hydrocarbon contained no cyclohexene at all; its compositionby gas chromatographic analysis was 35 percent benzene d Water contentof the alcohol, PdCh and GU01: system, approximately 0.6% by volume.

8 None detectable.

furan was 94%, and the yield of 3-ethoxy-2,5-dihydrofuran was less than1%.

3,3-diethoxyfuran is the stable fietal of tetrahydrofuran(dihydro3(2H)-furanone) is useful as an intermediate in the synthesis ofpyridoxine (Vitamin B-6).

Example 22 1 3 Example 23 To 200 ml. ethyl alcohol containing 5.00 g.palladous nitrate, an excess of sulfur dioxide was stirred in, tosaturate the alcohol to 30 p.s.i. Water content of the reaction mixture,exclusive of S was approximately 0.3 percent. The reaction mixture wasthen warmed to 50 and stirred at the temperature for 60 minutes. Themixture was then cooled, the excess surfur dioxide vented, and theliquid phase collected and analyzed by gas chromatography. A singleproduct was found, namely, diethyl sulfate, identified by the exactmatching of its residence times on two different columns (polyphenylether, 20' x at 175 C., and apiezon L, 8 x A" at 100 C.) with authenticreagent diethyl sulfate. The amount of diethyl sulfate found was 6.5g./liter, corresponding to a 39% conversion, based upon chargedpalladium salt.

Example 24 To 150 ml. of reagent anhydrous ethyl alcohol was added 3.47g. palladium (II) nitrate (0.100 mole/liter). Water content of themixture was approximately 0.2 percent. The mixture was stirred in aglass gas-sparging tower. A steady trickle of carbon monoxide gas (aboutml./ min.) was passed through the stirred mixture for three hours atroom temperature (26 C.), in the course of which time a palladium mirrordeveloped on the walls of the vessel. Analysis of a liquid sample showedthe formation of less than 0.05% of diethyl carbonate. The mixture wasthen warmed to 50 C. by means of infrared lamps and the carbon monoxidetrickle was continued for two hours, whereupon the mixture was analyzed.The major product, formed to the extent of 0.30% of the total mixture(25% conversion based on the total palladium salt charged), was diethylcarbonate, identified by vapor phase chromatography.

Example 25 50 ml. of an ethylene glycol solution containing 0.025 MPd(NO and 0.125 M Cu(NO .3H O were heated to 60 C. for two hours under33.5 atmospheres (absolute) pressure of carbon monoxide (CO), and withcontinuous agitation. Water content of the reaction mixture exclusive ofCO was about 1.2 percent. The resulting reaction mixture was then cooledand analyzed chromatographically. A quantitative conversion to 0.15 M ofethylene carbonate was obtained. No side product was detected.

It is to be understod that many modifications may be made within thescope of the present invention without departing from the spiritthereof, and the invention is intended to include all suchmodifications.

I claim:

1. A stable, homogeneous solution comprising:

(a) a compound of a noble metal of Group VIII of Mendeleeffs PeriodicTable, having a concentration of metal ion between about 0.01 and 0.0001mole per liter; and

(b) a major amount of an aqueous monoor poly-hydric alcohol containing(c) from about 0.1 to about 12 percent by volume of water.

2. A solution defined by claim 1 containing a promoter having anoxidation potential sufiicient to change the valence of the reducednoble metal to a higher valence state, the promoter being present in anamount of between about 0.1 mole to about moles per mole of noble metalion.

3. A solution defined by claim 2 wherein the promoter comprises Cu(BF 4.A solution defined by claim 2 wherein the promoter is selected from thegroup consisting of chlorides, bromides and iodides of a metal of GroupsVIII or I-B of Mendeleeffs Periodic Table.

5. A solution defined by claim 4 wherein the promoter comprises cupricchloride.

6. A solution defined by claim 2 wherein the promoter comprises cupricnitrate.

7. A solution defined by claim 1 wherein compound (a) is palladouschloride.

8. A solution defined by claim 1 wherein the alcohol (b) is methylalcohol.

9. A solution defined by claim 1 wherein the alcohol (b) is ethyleneglycol.

10. A solution defined by claim 2 wherein the promoter comprises cuprictrichloroacetate.

References Cited UNITED STATES PATENTS 3,106,579 10/1963 Hornig et al.252429 X-R 3,119,874 1/1964 Paszthory et a1. 252-429 XR 3,119,875 1/1964 Steinmetz et al. 252429 XR 3,121,673 2/ 1964 Riemenschneider et al.

252429 XR 3,122,586 2/1964 Berndt et al. 252-429 X=R PATRICK P. GARVIN,Primary Examiner.

